Single bar bed, tailstock alignment problem.

I have recently purchased a SIP 36" lathe. It has a single bar bed with key underneath to align the head and tailstocks. The tailstock keyway has quite a bit of play in it and this play is taken up by a pin, grubscrew and locknut. To align the tailstock I position it so that the tailstock centre and drive centre are in line and then adjust the pin/grubscrew. Problem is that the pin/grubscrew needs to be so tight that the tailstock will not slide on the bed and if it is any slacker then there is sideways movement in the tailstock and misalignment. Has anyone experienced this problem and how did you overcome it ?

"LesC" wrote: (clip) Has anyone experienced this problem and how did you overcome it ? ^^^^^^^^^^^^^^^ My Harbor Freight knockoff of the Sears monotube lathe had that same problem. I got rid of the problem by buying a better lathe. I also had trouble with the monotube rotating slightly, causing the tailstock to move off axis. It is held by a single setscrew (grubscrew), which is not secure enough.

I've used a lathe that's similar to this. Basically, you accept the tailstock being somewhat out of whack. Since you are not cutting with a fixed tool as in a metal lathe, a slight offset of the tailstock does _not_ automatically imply cutting a taper. Precision alignment is not really needed for spindle turning - it's nice, and buyng a better lathe is the way you get it, but it's hardly needed - consider all the crudely knocked-together wooden lathes of yore...

I have an old lathe which had a half-assed rebearing done that I have not corrected yet. It has a vertical misalignment of the tailstock center. Other than holes drilled from the tailstock being somewhat larger than the drill bit, it has not practical effect on turning - the only place it would be much of an issue would be on really short work mounted on a faceplate or chuck, which I can do with no tailstock. If you feel that you must use a tailcenter on faceplate work, it does have more of a need to line up "perfectly".

That gives me a warmer feeling about the tailstock of my wood lathe wobbling a few thousand of an inch or more. Come to think of it if the weldment construction or casting housing the bearings are not normalized after fabrication it will move and get the bearings out of line after a while. When making precision lathes to machine metal the entire lathe is normalized. Then the bearing housing is machined, honed and in line bearings are installed. The bed is then machined or better still hand scrapped to a set tolerance to maintain the perpendicularly and parallelism with the tailstock. I have doubt that when making lathe to turn wood the same procedures are used. For sure this tolerance is none existent with low end wood lathe. As for high priced lathe I welcome comments as to what standard the normalizing is done and to what tolerance the final machining is done.

I had a mono tube for a couple years. The play in the tailstock was not a major problem. For spindles it does not have to be aligned. For faceplate work I would mount the wood, then carefully mark the center on the tailstock side by either rotating it by hand and using a pencil to find center, or if it was fairly balanced I would run the lathe and use a skew to mark center. Then bring up the tailstock on the mark and you are aligned.

Les, If it is similar to the Sears monotube, you may be able to shim the rail that the tailstock registers against. Steel or brass shim stock from a good automotive jobber or machine shop supply house. They are available in sizes from .001" up. Cut to size and attach with CA glue AFTER assuring it will take up the slack without binding the movement.

Ken Moon Webberville, TX